The present invention relates to a condensing lens which condenses light components having desired wavelengths by reflecting and/or absorbing the other wavelengths components.
There has been proposed a system in which the sunlight is converged by a lens into a light conducting member to propagate therethrough to a desired location for lighting and other applications. For example, the converged light is usable for photosynthesis, that is, cultivation of chlorella or forcing culture of plants. In such an application, infrared rays and ultraviolet rays (and X-rays) contained in the solar energy are harmful for photosynthetic reactions. While the harmful light components may be removed by installing an optical filter in an optical path of the system, the filter renders the optical path intricate in structure and, because an optical filter capable of cutting both the infrared rays and the ultraviolet rays is unavailable at the present stage of development, two different kinds of filters are required which add to the intricacy of the optical path structure. Meanwhile, should an optical filter be located ahead or just past the lens with respect to the direction of light propagation, it would require an area identical with the area of the lens and, therefore, result in a bulky configuration. On the other hand, should the optical filter be positioned in the vicinity of the focal point of the lens, the filter would be damaged by the heat of the condensed light or a desired light component would be reflected by the filter to increase the loss, although the dimensions of the lens would be trimmed.
Meanwhile, it has recently been found that applying ultraviolet rays to plants which are ready for harvest promotes secretion of hormones of the plants, or maturing of the plants, thereby increasing the sweetness or giving better smell and/or color. Therefore, a light source apparatus is desired which, despite the use of an optical filter which usually cuts ultraviolet and infrared rays, allows ultraviolet rays to be supplied to plants only in the above-mentioned specific stage of cultivation.